Wes Stewart wrote:
On Mon, 06 Dec 2004 22:00:24 -0500, Mike Coslo
wrote:

|Cecil Moore wrote:
|
| Roy Lewallen wrote:
|
| My measurements, posted on this newsgroup some time ago and also
| published in QST's Technical Correspondence even longer ago, were for
| 300 ohm TV twinlead. The line was not lying on a wooden deck, nor did
| the measurements involve detergent of any kind.
|
|
| Who was it who published loss data based on laying the ladder-line
| on a wooden deck and/or squirting a wetting agent on it? Did you
| use a wetting agent?
|
| The N7WS experiment was accomplished by coating the line with a wetting
|agent.

No, the line wasn't "coated" with a wetting agent, a drop of
Microclean was added to a spray bottle of deionized water.

Wetting agent is as wetting agent does. You don't need much, but its
effects are dramatic.


|
| The wire was suspended horizontally, 12 feet of it.
|
| The author notes that it was "difficult to maintain uniform wetness"
|during the time it took to run the experiment. This would mean that he
|likely pooled water on the line.

No, I never said that either.


http://users.triconet.org/wesandlinda/ladder_line.pdf

Is my source.


The quoted text:

The reason for lower accuracy of we measurements is that it was
difficult to maintain uniform "wetness" during the several seconds it
took to make the measurements. Nevertheless, this lack of control is not
much different than the actual conditions a line might encounter in the
field.

end quote.


I'm assuming that you tried to maintain uniform wetness, hence the
judgment that it was difficult to do so.


For greater accuracy, 201
point-by-point measurements were made over the frequency range. This
takes some time, during which the moisture layer moved around (i.e.
was not uniform). This had the effect of corrupting the data
somewhat.

|
| And finally, I performed a little experiment. I have the ladder line
|from that antenna that was up for 2 years. Application of some water
|showed that it would bead up very nicely.

Bring your line out here to Arizona and leave it in the sun for two
years and re-run your experiment.



No, on second thought, don't come out here. There are too damn many
people moving here already and polluting the air with plasticizers.
At least Cecil left and went back to Texas.

|
| I just don't think the test conditions are very realistic. But it does
|tell me not to wash my ladder line with soap and water! ;^)

I stated, "The results of this are probably worse case and not
something that would necessarily be encountered in a typical
installation."

Also, if you would look at my "update" on my web site, you would see
the following:

"As an aside, I regret including so much about the wet condition. I
tried to make it clear that this was really worst case and not
something that would be seen in practice, but there has been so much
negative commentary about it, that it detracts from the point I was
trying to make."

I'll add you and Cecil to my list.

Gee Wes, I'm not trying to make a big argument with you! The experiment
was well conducted. But I do disagree with the initial assumptions. I
think wetting agent on a horizontally placed line is indeed worst case,
but it is a worst case that is not likely to ever happen in real life.
As you pretty much note.


And you are welcome to visit us here in beautiful Central PA any time
you like! 8^)

- Mike KB3EIA -

On Tue, 07 Dec 2004 16:23:58 -0500, Mike Coslo
wrote:

[snip]

| | The author notes that it was "difficult to maintain uniform wetness"
| |during the time it took to run the experiment. This would mean that he
| |likely pooled water on the line.
|
| No, I never said that either.
|
|
|http://users.triconet.org/wesandlinda/ladder_line.pdf
|
|Is my source.

I'm familiar with that source.
|
|
|The quoted text:
|
|The reason for lower accuracy of we measurements is that it was
|difficult to maintain uniform "wetness" during the several seconds it
|took to make the measurements. Nevertheless, this lack of control is not
|much different than the actual conditions a line might encounter in the
|field.
|
|end quote.
|
|
| I'm assuming that you tried to maintain uniform wetness, hence the
|judgment that it was difficult to do so.

As I said previously (below), "uniform" in this case meant "unchanging
during the measurement". With an A/C duct blowing dry air on the
sample, it was difficult to do.
|
|
| For greater accuracy, 201
| point-by-point measurements were made over the frequency range. This
| takes some time, during which the moisture layer moved around (i.e.
| was not uniform). This had the effect of corrupting the data
| somewhat.
|
| | I just don't think the test conditions are very realistic. But it does
| |tell me not to wash my ladder line with soap and water! ;^)

I guess I fail to understand what "realistic" conditions should apply.
Should I have taken a $250K analyzer out to your back yard or Cecil's?
[g]

The situation was thus:

I had a day job, trying to keep AMRAAM, TOW and Tomahawk missiles
flying. If I and the equipment weren't otherwise tied up, I could
make a few "personal" measurements.

I didn't measure only one sample, but five different lines, including
the open wire control.

The measurements were made in a 16' x 20' shielded room with an 8'
ceiling. This, the equipment placement and the need to access both
ends of the lines, unfortunately limited the length of the samples and
other factors dictated the frequency range that was usable.

The lines had to be taut, since the open wire line had no spacers
other than at the ends.

Horizontal seemed logical since any other orientation brought the ends
closer to the metal walls of the room or allowed the open-wire
conductors to sag toward each other.

I started with no, zip, nada, zero "initial assumptions", other than
the stated belief that hams tend to think that these lines are
lossless in almost any application and that I could make decent
measurements and find out. I had no ax to grind. I personally don't
use window or open-wire lines, preferring Heliax and resonant antennas
instead.

Wetting the lines was almost an afterthought. I remembered Roy's
Technical Correspondence on the issue and other anecdotal reports and
thought I would take a quick look. (With Roy's permission, I will put
a .pdf of this on my site)

|
| I stated, "The results of this are probably worse case and not
| something that would necessarily be encountered in a typical
| installation."
|
| Also, if you would look at my "update" on my web site, you would see
| the following:
|
| "As an aside, I regret including so much about the wet condition. I
| tried to make it clear that this was really worst case and not
| something that would be seen in practice, but there has been so much
| negative commentary about it, that it detracts from the point I was
| trying to make."
|
| I'll add you and Cecil to my list.
|
| Gee Wes, I'm not trying to make a big argument with you! The experiment
|was well conducted. But I do disagree with the initial assumptions. I
|think wetting agent on a horizontally placed line is indeed worst case,
|but it is a worst case that is not likely to ever happen in real life.
|As you pretty much note.

Yeah, pretty much.

| And you are welcome to visit us here in beautiful Central PA any time
|you like! 8^)

Thanks but I spent a week in PA once going to a corona measurement
course. Flew all day on Easter Sunday to get there and when I got
settled into the hotel I was greated by and experienced my first
earthquake. I don't know whether to come back or not. [g]